In order to elucidate the cellular site and molecular mechanism of 02 chemoreception within the carotid body I plan to: 1) develop tissue culture systems for growth of carotid body cells in isolation and in co-culture with sensory nerve cells, and to generate immortal lines of carotid body cells by cell fusion and tumor cloning techniques; 2) investigate the electrophysiological responses of these cells to simuli such as low oxygen tension and to evaluate the nature of their synaptic interaction with sensory neurons; 3) study the biochemical nature of the neurotransmitter in the isolated and immortalized carotid body cells under normal and chronically stimulated conditions; 4) generate monoclonal antibodies to the carotid body to use in concert with the physiological studies in order to distinguish subpopulations of carotid body cells, and to use in the isolation of molecules involved in the processes of O2 chemoreception. The role of the carotid body in ventilatory control in both normal and pulmonary disease states is well known, as is its tendency to hyperplasia and tumor formation with chronic hypoxic stimulation, and recent evidence suggest that it is involved in the sensation of breathlessness, in the drive to awake if there is airway obstruction, and in the pathophysiology of the sudden infant death syndrome. In addition, knowledge of the molecular basis of chemoreception may shed some light on the origin of sensations from within the body related to O2 deprivation, such as breatlessness, claudication, and angina.